There are many areas in which materials that provide thermal insulation are required. The exploration of space requires new technologies for long term cryogenic propellant storage applications in space, on the lunar surface, and on the earth. Thermal insulating materials help to lower the energy requirements to keep a substance hot or cold. High performance thermal insulation materials are needed to insulate cryotanks at both low and high temperatures on launch vehicles as well as cryogenic fluid storage tanks.
Further, reusable and cost effective insulation materials are of high interest in many industries. One example is the space industry where reusable, safe, reliable, lightweight and cost effective components in launch vehicles and spacecraft components are desired. Of particular interest are reusable launch vehicles (RLVs) designed to reduce the cost of access to space thereby promoting creation and delivery of new space services and other activities that can improve economic competitiveness. A target area for furthering this technology lies in design and development of reusable integrated insulation systems comprising lightweight composite materials. For example, cryogenic tank insulation materials currently employed provide sufficient thermal performance but are far from optimizing weight reduction and are not stable enough for integration into RLVs. Examples of these materials are organic foams based on polyetherimide, polyurethane, polyimide and other such compounds.
Silica aerogels are the best known thermal insulating materials available. However, the mechanical strength of these aerogels needs to be improved to meet the requirements of these applications. Improvements in the strength of aerogels would allow these materials to be used as advanced non-compacting insulation materials capable of retaining structural integrity while accommodating larger operating temperatures ranging from cryogenic to elevated temperatures.
Many silica containing aerogels crosslinked with organic polymers have been disclosed; see, for example, US Patent Application No. 2006/0286360 and U.S. Pat. No. 7,691,912 to Rhine et al. The mechanical strength of aerogel materials can be increased by reinforcing them with organic crosslinking agents. For example, polyimide materials have excellent thermal, mechanical and electronic properties compared to other organic polymeric materials, due to the highly rigid molecular structures. U.S. Pat. No. 7,074,880 to Rhine et al. discloses polymeric imides to which poly(dimethylsiloxane) has been attached and U.S. Pat. No. 7,074,880 to Rhine et al. discloses polyimides which are modified with silica, alumina and the like. In these disclosures, a majority of the materials are organic in nature. As such they deviate significantly from silica based aerogels. Based on previous results, it is not clear what properties a non-polymeric organic silica composite would have in terms of its mechanical strength in combination with its thermal insulating properties.
Therefore, there remains a need for light-weight silica aerogels which incorporate the excellent thermal conductivity properties of silica aerogels while incorporating the mechanical strength provided by organic crosslinking materials.